This invention relates to a pallet tray for transporting and storing workpieces in an automatic feed system attached to a machine tool, and particularly to such a tray having a common base member provided with recesses for the mounting of plastic inserts having holding pockets to accommodate individually configured workpieces.
A system for the feeding, withdrawal and reinsertion of such workpiece carrying pallet trays is described in Swiss Pat. No. 570,237. The workpieces occupy positions oriented in accordance with the production requirements, and are thus supplied to the loading and unloading stations of the machine tool. Each workpiece is taken in sequence from the pallet tray and, after its machining has been effected, it is placed back on the tray in its original position and orientation. The pallet trays are arranged parallel to each other at regular intervals on a conveyor system, and are advanced in steps under the control of a timing pulse generator. The system has automatically activated means for lifting each individual pallet tray from the conveying system or for sliding the tray off of a guide rail. Further means are provided for supplying the pallet tray to the loading and unloading stations of the machine tool, for passing it through the tool positions in a timed manner, and for returning the tray, carrying the machined workpieces, to the conveying system or to a guide rail thereof.
The pallet tray disclosed in Swiss Pat. No. 570,237 comprises a solid, unitary body made of a wear resistant plastic material. The high wear resistance is especially required owing to the heavy demand on the holding pockets for the workpieces since they are subjected to many cycles during which the workpieces are inserted and removed. With such plastic pallet trays attention must be given to maintaining all of the wall thicknesses as identical as possible and to avoiding material accumulations in order to prevent or minimize the warping of the trays during their production and subsequent use. This requires that separate pallet trays must be produced for each different sized holding pocket that is required, however, owing to the many differently configured workpieces that must be accommodated. It is thus not sufficient to just replace the inserts required for the different holding pockets at the injection mold, but instead a separate and costly mold must be provided for the manufacture of each differently dimensioned pallet tray.